More from WebMD

June 3, 2010 -- Can't start your day without a coffee? It's all in your mind, according to University of Bristol, U.K. researchers who've found the stimulating effects of caffeine may be just an illusion.

Their study involved 379 brave volunteers who went coffee "cold turkey" for 16 hours before being given a caffeine capsule or a placebo capsule containing corn flour.

They were then tested for a range of responses, but there was little variation between the real- caffeine group and the placebo group in levels of alertness.

Around half of the study participants were non-coffee drinkers or low consumers. The rest were medium to high consumers of coffee.

They were asked to rate their personal levels of anxiety, alertness, and headache before and after their drink -- which was either the caffeine or the placebo.

They were also given a series of computer tasks to test memory, attentiveness, and vigilance.

The medium/high caffeine consumers who had the placebo caffeine reported a decrease in alertness and an increase in headache, neither of which were reported by those who received caffeine.

However, their post-caffeine levels of alertness were no higher than the non/low consumers who received a placebo, suggesting caffeine only brings coffee drinkers back up to "normal."

The researchers also found people with a gene variant linked with anxiety tended to consume slightly larger amounts of coffee than those without the variant, suggesting that a mild increase in anxiety may be a part of the pleasant "buzz" caused by caffeine.

The study shows that frequent coffee drinkers develop a tolerance to both the anxiety-producing effects of caffeine that can put you on edge and the stimulating ones.

Heavy coffee drinkers may feel they are made alert by coffee, but the evidence suggests that this is just the reversal of the effects of acute caffeine withdrawal, which cause fatigue.

The researchers say that given the increased risk of anxiety and raised blood pressure brought on by caffeine, there is no net benefit to be gained.

Study researcher Peter Rogers, from the University of Bristol's department of experimental psychology, says in a news release: "Our study shows that we don't gain an advantage from consuming caffeine -- although we feel alerted by it, this is caffeine just bringing us back to normal. On the other hand, while caffeine can increase anxiety, tolerance means that for most caffeine consumers this effect is negligible."

What about decaf? Rogers tells WebMD by email: "Decaf wouldn't work -- without the caffeine one would get caffeine withdrawal (feelings of fatigue and headache) for a few days. In our study we gave pure caffeine in a capsule, with the placebo being corn flour in a capsule."

And does the researcher follow his study's findings?

"I'm a decaf coffee and tea consumer these days."

The study is published online in the journal Neuropsychopharmacology.

SOURCES:News release, University of Bristol.
Peter Rogers, University of Bristol.Neuropsychopharmacology.